It was not their only name change, incidentally; they were originally known as "the Mystics" -- not to be confused with the better-known Mystics who hailed from Brooklyn, NY, Hushabye -- when they began singing together in 1959, but the name may have brought them luck as their biggest hit came a year later under the new moniker. I Do (pop number 37/R&B number seven) was written by the group members as a warm-up song; something to sing to prepare their voices for live performance.
Around 1966, Jesse Smith left the group and was replaced by Andrew Thomas. The Mighty Marvelows' only other single of note was In the Morning, which climbed into to the R&B Top 30 (number 24) in the spring of 1968. Subsequent singles failed to chart. ABC/Paramount issued their self-titled LP that same year.
The Mighty Marvelows eventually disbanded in 1969, then reformed briefly in the mid-'70s as an oldies revival group, appearing to perform I Do during CBS-TV's late-'70s high school drama The White Shadow. In 1982, a live version of I Do was a hit for the J. Geils Band (pop number 24). ~ Bryan Thomas, Rovi